The present invention relates to a method for controlling the speed of a motor vehicle and the distance of the motor vehicle to at least one motor vehicle driving ahead, in which at least the speed of the motor vehicle and the distance to the motor vehicle driving ahead are determined with the aid of a detector having a distance sensor, and in which the driving speed is adjusted in response to detected distance a deviating from a setpoint trailing distance.
A method and a braking device for automatically decelerating a motor vehicle driven by a person is known from DE 196 47 430 A. In this context, the speed relative to an obstacle situated in front of the vehicle, approximately in the direction of travel, and the distance between the vehicle and the obstacle, are ascertained. The ascertained distance is compared to a vehicle braking distance for a speed that approximately corresponds to the relative speed. An automatic braking action is at least partially carried out as a function of the result of the comparison, when the ascertained distance is less than the specified braking distance.
In addition, DE 197 29 613 A describes a driving-support system for vehicles, by which a driver is instructed to pay attention to a vehicle driving ahead when a vehicle approaches the preceding vehicle and the distance between these two vehicles becomes smaller than a safe vehicle distance, this safe vehicle distance being established in two stages in accordance with traffic conditions. One stage corresponds to a state of low traffic density, in which the road is free or has little traffic or is not frequently used, and the second step corresponds to a state of high traffic density, in which the road is crowded or heavily traveled. Since, in the state of high traffic density, the safe vehicle distance is set to be less than that for the state of low traffic density, the frequent output of a warning signal due to the smaller safe vehicle distance is prevented when the road is heavily traveled.
The above-mentioned method for controlling the speed and distance of a motor vehicle is based on the problem that the methods known from the related art immediately start to control the distance when a new object, i.e. a new motor vehicle driving ahead, is detected by the detector. In this context, it is not taken into consideration that, since the control object may be traveling in another lane, the newly detected object may not represent an actual control object for the controlled motor vehicle. This especially occurs during cornering, where the motor vehicle is driving in the passing lane and a new control object is detected, which is traveling in the right lane and only ends up in the detection range of the detector due to the shape of the curve. Therefore, the present invention is based on the engineering problem of specifying a method, which controls the speed and the distance of the motor vehicle to at least one motor vehicle driving ahead, in a manner that is simpler and, at the same time, more reliable.
The above-mentioned engineering problem is solved by a method of the present invention according to claim 1, in that an intervention distance ai, which is less than the range of the distance sensor, is determined, and that traveling speed v is adjusted at a distance a, which is less than intervention distance ai. As long as the new control object is situated between the radius of action of the distance sensor and the intervention distance, the use of the described intervention distance allows the control object to be initially monitored, in order to ascertain its driving behavior. The distance is only controlled in a customary manner, when the distance falls below the intervention distance.
The maximum intervention distance is preferredly defined to be less than 90%, preferably less than 80%, and especially less than 70% of the range of the distance sensor. Therefore, the distance range in which the control object is only monitored without the motor vehicle being controlled, lies in the area of 10 to 30% of the range of the distance sensor, so that a sufficient monitoring time is provided for all driving situations.
It is particularly preferable for the intervention distance to be determined as a function of the relative speed of the motor vehicle and a motor vehicle driving ahead. This is based on the realization that, for different relative speeds, different braking times are required for adjusting the distance of the controlled motor vehicle to the safe distance given. Large relative speeds require a longer braking time, while smaller relative speeds require shorter braking times.
In a further, preferred manner, the intervention distance is calculated as a continuously increasing function of the relative speed, the function being either a linear or a nonlinear function. In the case of a linear function, the intervention distance, starting from a minimum intervention distance, linearly increases according to a preset slope, as a function of the relative speed. In the case of a nonlinear function, the slope is greater for low relative-speed values than for high relative speeds. Finally, it is recognized that the braking distance increases superproportionally to the relative speed, since the traveling energy is a quadratic function of the traveling speed. In comparison with a linear function, the described, nonlinear curve of the function tends to cause higher intervention distances to be calculated for increasing values of the relative speed.
Because of the same idea that the kinetic energy quadratically increases with the traveling speed, the values for the minimum intervention distance and the maximum intervention distance are calculated in a further preferred manner, as a function of the traveling speed.
It is equally possible to calculate the values for the minimum intervention distance and the maximum intervention distance as a function of the type of road that is used. In so doing, the type of road may be input by the user or determined, using the frequency of curves driven through per unit time, or using data of a positioning system, preferably a global positioning system (GPS). Since one normally travels at higher speeds on expressways than on country roads or even urban roads, the intervention distances may be determined as a function of the type of road used.